Experimental study and kinetics modeling of partial oxidation reactions in heavily sooting laminar premixed methane flames

The partial oxidation (POX) of methane in heavily sooting laminar premixed methane/oxygen flames was studied with an emphasis on acetylene formation and depletion. The flame temperature profiles were measured with a Pt/Pt-Rh thermocouple coated with Y ₂O ₃-BeO ceramic. Gas species along the flame axis were sampled by a quartz probe for their concentrations to be measured by a mass spectrometer. The problem of soot deposition on the sampling probe was overcome by in situ cleaning of the nozzle orifice. The mole ratios of O ₂/CH ₄ in the experiments were 0.55, 0.60, 0.65 and the STP (standard temperature and pressure) reactant flow velocity was fixed at 4cm/s. Computational results based on the Curran, Wang-Frenklach and GRI 3.0 detailed chemistry mechanisms were compared with the experimental results. The values predicted by the Curran and Wang-Frenklach mechanisms for the reaction conditions of this study were within the acceptable range. The maximum concentrations of acetylene were positioned in the flame area at 4-8mm distance from the burner, and were behind the positions of the maximum mole fractions of ethane and ethylene. Much more diacetylene and benzene were generated in the post-flame area than in the flame. Recombination reactions to larger hydrocarbon molecules and oxidation with hydroxyl radicals in the post-flame region were the main reactions responsible for acetylene depletion in the fuel rich methane flame.